Ceramic aerogels are among the most highly porous and lowest density materials. Their high porosity means that 95% or greater of the total bulk volume of a ceramic aerogel is occupied by empty space or air, producing excellent thermal as well as sound insulating qualities. In addition, their high specific surface area (e.g. on the order of 600-1000 M2/g the aerogels are well suited for numerous other applications. Unfortunately, however, conventional ceramic aerogels are physically and hydrolytically very unstable and brittle. Their macro-structure can be completely destroyed by minor mechanical loads e.g. vibrations or by exposure to moisture. Consequently, there has been little interest in ceramic aerogels for the above-mentioned reasons, despite their excellent properties, simply because aerogels are not sufficiently strong to withstand even minor or incidental mechanical stresses to be experienced in practical applications. Therefore, these aerogels have been used almost exclusively in applications where they experience substantially no mechanical loading. However, cross-linking silica-aerogels with a polymeric material has proven to be an effective process to increase the strength of these aerogels without adversely affecting their porosity and low density. Most of the present processes are very long and involved, requiring multiple washing and soaking steps to infiltrate the silica gel with the polymer monomer after gelation. In addition, infiltration is limited by diffusion, sometimes resulting in aerogel monoliths which are not uniformly cross-linked.
Thus, by cross-linking the epoxy polymer into the bulk structure of the silica gel, the resulting silica aerogel is reinforced while the mesoporous space between the particles is maintained. In the prior art processes, to provide polymer reinforced aerogels, the polymer crosslinker is reacted with the surface of the silica gel, because the silica particles are surface-terminated with reactive groups. Therefore, cross-linked aerogels are being prepared by polymerizing the prepolymer with the mesoporous surfaces of the silica gels in a two-step process.